Field of the Invention
The present invention relates to an anti-icing system that prevents icing on a leading edge of an aircraft, and to an aircraft including the anti-icing system.
Description of the Related Art
During flight of an aircraft, icing occurs on an outer surface of a leading edge in a traveling direction of the aircraft, such as a main wing, a tail wing, and an air intake, due to collision of supercooled droplets in the air. The icing phenomenon variously influences flight of the aircraft. Therefore, an anti-icing system that prevents icing by various heating means are provided at positions that may be particularly affected by the icing phenomenon.
In an aircraft including a turbine engine, as one of the anti-icing system, bleed air that is high-temperature high-pressure air extracted from an engine compressor has been widely used as a heating source. In such an anti-icing system, the bleed air is guided through a pipe and is blown to the inner surface of the leading edge, thereby performing heating. A member called piccolo tube that has, in the longitudinal direction, a plurality of ejection holes through which the bleed air is ejected is used as the pipe. For example, when being provided in the main wing, the piccolo tube is disposed near the leading edge along a wing length direction from an end connected to a fuselage toward a front end. As illustrated in FIG. 10A, the method makes it possible to provide high heat transfer coefficient at a blown point of the bleed air BA. This makes it possible to reduce an air supply amount and to suppress deterioration of fuel consumption, as compared with other methods.
In FIG. 10B, a solid line DD indicates distribution of the heat transfer coefficient of the bleed air, and a dashed line HD indicates distribution of collision of droplets. The drawing shows that the blown point at which the heat transfer coefficient of the bleed air shows a peak and an outside airflow stagnation point (hereinafter, simply referred to as a stagnation point) Ps at which the collision amount of the droplets shows a peak are coincident with each other.
As illustrated in FIG. 10B, the heat transfer coefficient is drastically decreased at a position away from the blown point at which the heat transfer coefficient shows a peak. Therefore, temperature unevenness easily occurs at the blown point and positions (P1 and P2) away from the blown point. If the positions of the respective ejection holes of the piccolo tube are not appropriate, disadvantageously, heating may become insufficient or damage of the leading edge structure caused by overheating may be accelerated. Therefore, focusing on particularly stringent icing flight condition, a method of orienting ejection holes to concentrate a heating amount to a stagnation point where a collision amount of the droplets shows a peak under the condition is typically used. When the flight condition, in particular, an angle of attack of the aircraft is varied and the position of the stagnation point is accordingly moved, however, the blown point, namely, a point to which the heating amount is concentrated is not coincident with the position at which the collision amount of the droplets shows a peak as illustrated in FIG. 10C, which deteriorates efficiency of heating. This may cause increase of the air amount necessary for anti-icing or may accelerate damage of the leading edge structure by overheating.
Therefore, Japanese Patent Laid-Open No. 2011-183922 suggests a method of configuring the inner surface side of the leading edge structure of the main wing as the double structure and averaging heat transfer coefficients. In addition, National Publication of International Patent Application No. 2009-523637 suggests means that promotes cooling by making a transition from a flow on an outer surface of the leading edge structure to turbulent flow, thereby preventing local overheating.
The suggestion by Japanese Patent Laid-Open No. 2011-183922, however, uses the double structure that is complicated. In addition, since the weight is increased and heat loss to the parts other than the part to be heated is large, it is necessary to increase the amount of extracted air, which may result in deterioration of fuel consumption.
Moreover, the suggestion by National Publication of International Patent Application No. 2009-523637 uses the structure that makes transition to the turbulent flow. The structure may increase, for example, air resistance of a main wing and accordingly cause deterioration of fuel consumption. In addition, since the cooling of the leading edge is promoted, the necessary amount of the heated gas may be increased.
Therefore, an object of the present invention is to provide an anti-icing system that has a simple configuration and makes it possible to exert anti-icing performance by dealing with displacement of a stagnation point without increasing air resistance.